Pipetting devices are widely used for dispensing defined volumes of liquids, especially in the range of around twenty milliliters down to picoliters. They are standard equipment in laboratories and widely used for example in the field of chemistry, biology, medicine and diagnostic. Depending on the concrete purpose different types of pipettes are known.
Glass pipettes in which the liquid is pipetted by mouth have been used in the past. Nowadays manual pipetting devices are used, which are for example commercially available from Eppendorf and Gilson. These can be single channel devices, but also multichannel pipettes are used allowing transferring several liquids at once. Most of these manual devices comprise a handle, a lower part used to transfer the liquids, a shaft connecting the handle with said lower part. In case a pipette allows to adjust the volume of liquid these pipettes also have means for adjusting the volume, for example by thumb wheels integrated into the handle. They also have means for generation of a vacuum allowing sucking the desired volume of liquid into the pipette, frequently this is a movable piston in a cylinder integrated in the pipette which can be moved by a push-down button at the upper part of the pipette.
As contaminations between samples or reagents are not desirable, many of these pipettes are used in conjunction with disposable tips. These tips are attached to a mounting surface at the lower end of the pipette and are discarded after use. The Pipette itself usually has no direct contact with the liquid. To simplify ejection of the tips several means are used by pipettes known in the art. Usually such ejectors are means which slip off the tip by applying pressure to the upper edge of the tip and which are connected to a push-down button at the upper side of the pipette.
Beside manual pipettes also automated pipettes are known. In the field of Chemistry, Biology and Medicine for example automated devices are used for sample preparation and diagnostic assays, which in most cases also have automated pipettes included. These pipettes either use tips which can be easily washed after use or which use disposable tips similar to those used by the manual devices described above.
Depending on the volume, which should be dispensed, the size of the disposable tips varies. Consequently, different pipettes having mounting surfaces of different diameters for the different tips are used. Whereas this might be acceptable when conducting manual experiments or assays, the need to use separate pipettes for disposable tips of different size represents a significant disadvantage for automated systems.
In U.S. Pat. No. 4,593,837 a pipette is described which has different mounting surfaces for mounting tips of different size. However, no means are described for this pipette which allows discarding the tips after use.
Thus, it was an object of the present invention to provide an improved pipetting device allowing the use of differently-sized tips, especially a device which allows to easily discarding the disposable tips after use.